This invention relates to analysis of materials, and more particularly, relates to method and apparatus for the reductive decomposition and quantitative determination of constituents of a sample.
A common form of sample preparation for elemental analysis involves the pyrolysis and reduction of a sample followed by the use of the resulting gases from this sample for the detection of the desired constituent(s) or analyte(s). Examples of this include nitrogen, halogen and sulfur determination using microcouloumetry, and sulfur determination by measurement of differential darkening of an absorber ribbon. There is a problem associated with the reduction process which can cause unreliable analytical results and this problem centers on the sample introduction step.
If the sample is introduced using a syringe needle the needle must be placed directly into or very close to the hot zone of the reduction furnace to ensure the sample is transferred into the pyrolysis zone and pyrolyzed and reduced therein. Unfortunately, heavy organic fractions or salts can remain within the needle and possibly clog it temporarily, or permanently. One approach taken to overcome this problem is to introduce the sample into the hot portion of the furnace using a small boat which has been loaded with the sample when the boat was positioned in a relatively cool portion of the furnace tube. In either case, however, the sample introduction and subsequent pyrolysis and reduction is a transient process. Therefore, the hydrogen concentration in the reduction tube changes over time during this process. This can be detrimental in cases where equilibria involving hydrogen are important to the instrumental stability, sensitivity, or detection limits.
Accordingly, there is a need for a sample introduction scheme to allow for longer integration times in the detection phase which would then improve detection limits and also allow for use as an on-line monitor in process control, or as a chromatographic detector.
These and other limitations and disadvantages of the prior art are overcome by the present invention, however, and improved methods and apparatus are provided for decomposition and analysis of samples.